EP0204295A2 - Measuring device for determining wind direction and wind speed in the atmosphere - Google Patents

Abstract

To determine the wind direction and wind speed in the atmosphere using a LaserDoppler anemometer, only measured values from a sector of approximately 100 ° and less of an azimuth scan are fed to a multiple peak finder of a measuring device; In order to achieve a high processing speed, there is a fluid differentiation using digitally working devices. The measuring device is used to switch off influences caused by clouds, haze, fog, etc. originate in the multiple peak finder always pursuing several frequency maxima, in each case a preceding maximum being related to a subsequent maximum until the subsequent maximum is smaller than the previous maximum. Due to the achievable, fast sector scanning, the measuring device can be used particularly advantageously when determining multiple wind peaks caused by clouds and / or fog echoes, or at a location where the measuring range is very limited, or also when detecting vortices use and use very advantageously.

Description

The invention relates to a measuring device for determining the wind direction and wind speed in the atmosphere according to the preamble of claim 1.

The applicant has already developed a continuous wave laser Doppler anemometer (which will be referred to as an LD anemometer for the sake of simplicity) for the measurements of wind boundary layers, with which the horizontal wind, namely its two components, and the wind profile at different Weather conditions can be measured by a full scan or scan over an azimuth angle of 360 ^* at different elevation angles (research report DFVLR-FB 83-11). The results achieved with this LD anemometer were compared with conventional balloon probe profiles, for example at heights of at least 250m to 750m and higher. It was found that the wind profiles determined with the LD anemometer in the first 750m are more typical of the d-average wind profile than profiles derived from probe measurements, since the LD anemometer itself creates a spatial mean value.

A block diagram of such a conventional LD anemometer published in DFVLR Announcements 79-18 is shown in FIG. The conventional anemometer uses a transceiver with an aperture diameter of 30 cm and a scanning system with two mirrors SP1 and SP2. Two collimator lenses KL are used for distance scanning intended. The range resolution is 6m with a focus set to 100m. The radiation from a local oscillator and the Doppler-shifted signal from the measurement volume are mixed on a detector after passing through an interferometer. An SAW acoustic surface wave spectrum analyzer is used to process Doppler shifted signals.

A single radial speed spectrum can be obtained within 50ps and an integrator enables averaging over 50ms. The signal is input to an oscillograph and a processor for data readout and storage.

Because of atmospheric inhomogeneities, especially near the surface of the earth, a wind field is generally not the same at all points of a full scan for a speed azimuth display (which for the sake of simplicity is also referred to below as VAD scan). It is therefore common to compare speed profiles obtained from different sectors during the scan for agreement. Measurements of the wind strength and direction up to a height of 750 m carried out with the LD anemometer, which were generated from radial speed data on only a part of a full azimuth circle, were preferably compared with measurements obtained from a full circle scan.

In the invention, this, above all, time-consuming comparison of values obtained from sectors with values obtained by a full scan is to be omitted. The invention is therefore intended to provide a measuring device for determining the wind direction and speed in the atmosphere, with which a wind profile can be obtained with approximately the same degree of accuracy as in the case of a full circle, even in the event of a handicap or restriction due to local or spatial conditions at the installation site of the measuring device Scanning or scanning, but in a significantly shorter time and thus much faster and less time consuming to create.

According to the invention, this is achieved in a measuring device for determining the wind direction and speed in the atmosphere by the subject matter of claim 1. Advantageous developments of the invention are specified in the subclaims.

In the measuring device according to the invention, for example, the measuring time for a scanning or scanning over a quarter circle sector is in the order of magnitude of 12s. However, due to the use of a multiple peak finder, useful speed estimates of the wind are already possible with sector scans up to 1/16 of a circle, with a weighted adaptation program for the least squares preferably also being used in order to analyze the radial speed against azimuth data. The influence of clouds and fog on wind measurements carried out with the measuring device according to the invention is evident from the data obtained in practice. This influence can be greatly reduced with the help of visibility and cloud height information in conjunction with a finer analysis of the actual speed spectrum than is possible, for example, with a single peak finder. The data system downstream of the measuring device according to the invention was adapted to the requirements for sector scanning and with regard to the multiple peak finder used in all-weather conditions.

A modified measuring device according to the invention can also be used and used for boundary layer investigations, for contamination monitoring, for ballistic investigations, in particular if parts of the atmosphere are covered, for example, by trees or hills. There is also information regarding the Windpro in other areas fils is useful or desired, such a special application of the measuring device according to the invention is the detection of so-called vortex wakes, which are generated by large aircraft during landing.

The invention is explained in detail below on the basis of preferred embodiments with reference to the accompanying drawings. Show it:

• Fig.l is a block diagram of the optical and electronic part and the evaluation part of a continuous wave Doppler anemometer;
• 2a shows perspective representations of scans with a speed azimuth display (VAD display) at different elevation angles;
• 2a shows a projection onto the surface of the earth of the scans reproduced in FIG. 2a;
• 3 shows a block diagram of a fast-working data system;
• 4 shows a Doppler spectrum in a digitally reproduced field;
• 5 shows a computer printout of a speed spectrum at an elevation angle of 30 ° at a distance of 350 m at an azimuth angle between 310 ° and 50 °;
• 6 shows a sector scan sine wave adaptation for three different heights in fog and cloud conditions;
• 7 shows a location of an LD anemometer housed in a container on a platform in the North Sea, the field of vision being entered;
• 8 vertical wind profiles for an LD anemometer sector scan measurement, a hypothetical, logarithmic wind profile being entered for comparison;
• 9 shows a representation of the basic formation of vortices in a landing aircraft;
• Fig.lOa a basic illustration of a vortex measurement with an LD anemometer;
• 10b shows a curve in which the tangential vortex wake speed is plotted;
• Fig.lOc rectified vortex profiles in a homodyne LD anemometer;
• Fig.ll a computer printout of information of about 50 blocks from a special memory, and
• Fig.12 is a computer printout of an experimental vortex signature (+) and the best fit to a theoretical model (o) for the same example as in Fig.ll.

Heterodyne Doppler LD anemometers measure the radial component of the wind, ie the speed component along the line of sight or the line of sight of the LD anemometer. A distance, azimuth and elevation angle scan is required to determine the size and direction of a horizontal wind. For this purpose, the average horizontal wind strength and direction can be determined from radial speed data along horizontal circles which are centered with respect to the vertical axis of a scanning device or a scanner. By changing the height of the circles, vertical profiles of a horizontal wind can be measured. This measuring method is referred to as conical scanning or scanning because the measuring beam passes through a cone whose the tip of which is at the bottom of the scanner. Since the data as a function of the scanning azimuth consists of radial speed values, the method is also referred to as a speed azimuth display scan (or VAD scan for short).

2a shows various VAD scanning cones of this type at different elevation angles and at different distances, a so-called VAD sector scan being entered on the individual scanning cones by means of a double line. At the same time, buildings are shown schematically in FIG. 2a, which represent an obstacle at small elevation angles, in the direction of which it cannot be scanned. In FIG. 2b the area covered by the buildings is indicated by a thin wavy line at low elevation angles. Furthermore, in the top view of FIG. 2a, FIG. 2a shows the projection of a VAD scan onto a horizontal plane with respect to the expansion of the combustion volume, i.e. the sensitive area, hatched.

As already mentioned and shown in Fig. 2a, scanning with an LD anemometer is possible in certain azimuth areas, for example through buildings, trees or through hills and the like. hindered, so that only part of a scan, which is then not centered over the LD anemometer, provides usable data.

However, such wind values, which are derived from scans over a part of a full circle, are quite representative of the wind conditions in this scanning area, as extensive theoretical studies and practical tests by the inventors have shown. However, in order to implement a usable scanning pattern, a very special control method is required; a block diagram of such a method is shown in FIG.

In laser technology, the received signals of a

Scattered laser light so-called signal transients are obtained, which correspond approximately to a 1 / x ² function and can contain different numbers of target echoes, these target echoes are impressed as signal peaks of the 1 / x ² function. In most practical applications, it is of interest to determine the amplitude and delay of the signal peaks in relation to the emitted laser light pulse as quickly as possible.

With the help of the peak value amplitude and the light propagation time, the reflectance and the distance of the targeted target can be determined. To quickly evaluate the peak signal values of interest, the received transient of the backscatter signal is examined for occurring maxima. For this purpose, the turning points of all peak values are determined.

This process must be carried out independently of the basic echo curve, i.e. a differentiation of the peak values or the peaks may only relate to these and must disregard the course of the basic transient function, such a "flowing differentiation" having to be carried out with regard to high processing speeds by means of digitally operating devices.

For this reason, the backscatter or echo signal is digitized using an analog-to-digital converter (ADC) and stored in a memory. This function, which is to a certain extent frozen, can now be read out point by point and fed to the peak finder. In the peak finder fed with this information, a previous measured value is compared with a subsequent one and it is determined whether the subsequent value is greater than the previous one. This process is carried out repeatedly until the subsequent measured value becomes smaller than the previous one. At this point, the evaluation electronics stops the search run and determines the amplitude and runtime for a registration a mass storage device such as a magnetic tape.

This evaluation method has the advantage that parts of the echo signal curve that are not of interest are scanned extremely quickly, and evaluation and data determination and output only take place if a signal peak is found, the amplitude size of which plays no role in the evaluation, since this is the decisive criterion is the turning point of this peak. In this case, this method is applied to arbitrary signal profiles which contain information which, because of their turning points, is significant for such an intended evaluation.

According to the invention, this method was used in conjunction with a multiple peak finder and the LD anemometer described at the beginning, which, as already mentioned, works with a continuous wave or CW laser and with which the wind speed is measured using the Doppler effect. Here, the signal peaks occurring in an echo signal indicate the wind speeds determined at a defined (focused) measuring point.

In this case, the evaluation mainly relates to the "Doppler frequency shift", which is proportional to the wind speed and behaves very similarly to conventional LIDAR backscatter signals in terms of the signal peaks in the electronic image representation of the backscatter signal. The position of the measured peak values on the time axis of a digital recording (see Fig. 4) corresponds to a precisely defined wind speed.

The LD anemometer has a mean value image with which it is possible to sum up to 1024 frequency spectra in order to improve the signal / noise ratio.

After completion of such an averaging process, the evaluation electronics takes over a spectrum and digitizes it in an analog-to-digital converter (ADC).

The digitized signal has a resolution of 6 bits for the full modulation range, which is limited to a signal amplitude of 1V. In a subsequent circuit, which consists of two random memories forming a so-called twin RAM, two successive values are taken from the memory of the last-mentioned analog-digital converter (ADC), temporarily stored in this twin RAM memory and according to the criterion examined whether the subsequent, ie the (n + 1) th value A is greater than the previous one, i.e. nth value B was. A digital comparator (COMP) connected downstream of the twin RAM memories has three decision outputs at which the respective ratio of the two values to be compared with one another is such that the following three statements, namely value A greater than value B, value A equal Value B and value A less than value B can be taken.

Here, the digital comparator (COMP) changes its value from a digital "0" to a digital "1" if the value A is greater than B (A> B), and it (COMP) only falls into its "0" - State back if the value A is neither greater than or equal to the value B. The digital transition from a digital "0" to a digital "1" can then be determined by means of an electronic differentiator (DIFF) which shows no reaction when the signal output changes from a digital "0" to a digital "1".

This differentiation results in a pulse by means of which an interruption in the evaluation cycle is initiated and a transfer of the significant peak or peak values, such as the amplitude and the time position, to another buffer or buffer memory (BUFF-RAM) is portable. A running counter registers the number of peak or peak values. After a complete examination of the respective spectrum for any occurring or occurring signal peaks, a so-called compact data transfer to a mass storage device takes place, for example in the form of a magnetic tape. Here, all data are read out from the buffer or buffer memory (BUFF-RAM) in a defined format and stored on the mass storage device, for example in the form of a magnetic tape, with the inclusion of further important system data (so-called house keeping).

In the case of an immediately subsequent or later evaluation in a downstream computer center, all measuring system parameters and the number of signal peaks to be evaluated, their amplitudes and their spectral position are then obtained. With the help of this method, which already processes very fast pre-classification processes during data recording, the evaluation in the downstream computer center results in a considerable reduction in evaluation time.

The entire measuring system is controlled by a computer, for example a CBM 8096 computer; interfaces, i.e. Interface units for the data and control part of the computer, for example a floppy disc CBM 8050 and a printer CBM 3023, can be compatible with an IEEE bus. The scanning device or the scanner are controlled by means of azimuth and elevation loops during the various scanning or scanning processes, for example the VAD technique or the elevation scan technique. In this case, all control signals are introduced into the system, for example via the keypad of the computer.

In the case of VAD measurements with full circle scans, the elevation angle and the number of azimuth revolutions transfer. With a fast sector scan, however, only part of a revolution is used and the corresponding azimuth angles are transmitted. In the case of an elevation angle scan, for example in the case of whirl vane tracking, an (imaginary) vertical scanning plane must be set up perpendicular to the runway direction. In this plane, a sufficient height between the earth's surface and the expected vortex trails is covered by a rapid elevation angle scan. The upper and lower elevation angle and the scanning speed can be selected accordingly by entering them on the keypad of the computer used. Then the elevation angle scan runs automatically.

4 shows a typical spectrum of a spectrum analyzer; the ordinate shows the signal voltage (U in volts) and the abscissa the wind speed (v _LOS in m / s). Parallel to the abscissa and ordinate, the corresponding digital values are given at the top and right edges. Here, the integrator of the LD anemometer shown in the block diagram of FIG. 3 serves as a data source; This integrator generates frequency spectra which are averaged over selectable time periods from 1.6 to 52 ms and which contain wind information. In particular, the peak position in the spectrum corresponds to the size of the radial wind components inside and outside the measurement volume. The components related to fog and clouds originate outside the measuring volume.

To reduce the amount of data to be transmitted, only the peak values of each spectrum are used. A special interface device or a corresponding interface selects the peak position in amplitude and speed channels using the digital differentiation method described above.

The amplitude of the wind peaks depends on the scattering part deviate in relation to the focused distance. The interface device referred to as the "write" interface in FIG. 3 selects the information from the distance, elevation and azimuth position and from the angle information in data blocks and writes a complete block via a format former into a tape recorder, for example of the Kennedy 8000 CCT type, every 50 ms Tape recorder. The respective block header contains the measurement distance and the number of peaks. (In Fig. 4 there are 6 peaks, for example). The block itself contains the amplitude as well as the radial wind speed of each peak. In this way 188 peaks can be determined. When using the LD anemometer according to the invention, since it is a homodyne system, the sign (+ or -) of the radial speed cannot be determined. The first peak shown in Figure 4 is the strong (not of interest here) zero frequency spectral peak.

In the case of a measurement campaign, the data determined can be examined with the aid of an additional “read” interface shown in FIG. 3 from the same computer that is used to write the data. This measure is necessary to make sure that all the data entered is correctly determined and entered. Furthermore, the level of the individual peaks, i.e. whose amplitude can be further optimized by noise level suppression.

• a) bei der Ermittlung von Mehrfach-Windpeaks, welche durch Wolken- und/oder Nebelechos hervorgerufen sind,
• b) bei einem Aufstellungsort, bei welchem der Meßbereich, d.h. das visuelle Segment, sehr begrenzt ist, und
• c) bei einer Wirbelschleppenerkennung.

In order to show the possible uses of the measuring device according to the invention, three examples are described below, in which fast sector scanning is particularly advantageous, namely

• a) when determining multiple wind peaks caused by cloud and / or fog echoes,
• b) at a location where the measuring range, ie the visual segment, is very limited, and
• c) with a vortex detection.

The data system used can store 20 blocks every second and has an azimuth angle resolution of 1 °, which means a minimum scanning speed of 20 ° per second.

(a) Determination of multiple wind peaks

When determining multiple wind peaks, the influence of clouds and fog on wind measurements with a C0 ₂ long-wave laser Doppler anemometer is known and described in the literature. In addition to the wind peak from the focused measurement volume, some other peaks originate from clouds or fog outside the focused area. When scanning in the azimuth direction, these peaks differ in their phase and speed behavior from the peaks originating from the measurement volume. 5 shows an example of a printout result of a computer during a fast scan over a range of approximately 90 °. In this case, the numbers given in FIG. 5 correspond to the digitized signal amplitude and their position to the line of sight speed (which can be seen in FIG. 4). A sector of slightly more than 90 'is shown in FIG. 5 and the letter "B" is a value for a sine formation corresponding to the curve denoted by the number 6.

5 also shows constant peak positions, which are caused by the system, as well as some additional noise peaks. Here, the amplitude value of 2 is close to the noise level. The rectified sine wave reproduces the wind signal (values 4 to 7), from which the azimuth dependence of the line of sight speed can be seen, from which the speed and direction of the wind field can be calculated. The column at the beginning of the curve display shows the azimuth, elevation and distance information for each block; the measurement shown in Figure 5 was carried out at an elevation angle of 30 'with a Focus range of 700m at an azimuth angle of 70 ° to 172 ° to the system axis.

The calculation preferably begins with the entry of the selected azimuth angle range in which the calculation is valid. Areas such as obstacles, masts, etc. that interfere with the measurement are not taken into account. Furthermore, the average, average wind direction is entered into the computer to find out the actual wind direction. Here, the angle of the axis of the measuring device to the north direction is necessary in order to be able to correct the wind direction in this way. Some filtering operations also need to be performed. The noise level (e.g. ≤ 2) reduces the number of valid, usable peaks. A matrix (A) is set up for each intensity (x ₃ = 0). In the next step, large deviations from a sine line are taken into account, values with very large deviations being separated and set to zero. After performing these steps, the condition x ₃ = 0 is no longer valid. The calculation is then started. 5 shows a sine line of the intensity value 6, which is designated by the letter B. Since this value B fits very well with the sine curve, it can be seen from this that the curve labeled with the intensity value 4 has a different phase, but almost the same speed.

6 shows part of the computer work for three different heights. The line of sight v _LOS plotted on the ordinate is shown in the three curves at 10 ° intervals over the azimuth angle plotted on the abscissa. The crosses entered in the diagrams each represent a valid peak with no further amplitude information. The recordings were made by a computer, the worst case for wind measurements carried out with the LD anemometer being shown, since there is a layer of dust on the ground and at a height of There was a layer of cloud at 850m.

The method for handling multiple peak information is also shown in Fig. 6. If the measurement is started from the first layer lying close to the ground to greater heights and the information dust or no dust or cloud or no cloud is entered into the computer, the computer can treat the information as an additional filter . In the computer printout of FIG. 5, the "stars" come from the dust layer information (with regard to speed and direction) and these values, which are identified by the "stars", fit very well with the curve corresponding to intensity 6 or the adaptation B.

(b) Measurements within limited visual segments

Often, the location of a measuring arrangement can only be "seen" in a limited sector of the sky. A wind vector for the boundary layer can be obtained with the measuring device according to the invention. For example, the wind profile over sea should be obtained from a floating platform. In a practical case, sketched in Fig. 7, a measurement had to be carried out from a point behind which masts and cranes stood and a helicopter landing platform was lying. The north sea view sector was approximately 120 _. . The possible field of view available is shown in FIG. 7 by the azimuth angle indications 310 ° to 56 *.

In Fig. 8 the measured wind profile is measured at two distances, namely 175m and 250m from the platform at heights from Om to 100m above the sea surface. The measured wind profile at a distance of 175m is shown with error lines regarding the height resolution and the wind deviation. There is no measured logarithmic wind profile, only the turbulence increases towards the sea surface. In Fig.8 there is still in the lower left part entered a hypothetical wind profile that was known from previous measurements. The measuring direction was in the lee of the platform. If the wind blows from the north, this does not affect long distances.

(c) Vortex pattern recognition

As already mentioned at the beginning, large aircraft generate very strong whirlwinds when landing, which can pose a danger to subsequent, in particular smaller, aircraft. Since the vortex towing problem can have a greater or lesser influence on the capacity of large airfields, in particular on the operation on parallel runways, knowledge of the path of the vortex towing formed is of great importance.

The formation and formation of vortices are shown schematically in Fig.9 and in Fig.lOa to c using curves. A landing large plane creates a pair of vortices. With a cross or cross wind of 0 or 2m / s, the theoretical propagation curves for the right tow are shown by solid lines and for the left tow by dashed lines.

A vertical, imaginary scanning plane is defined perpendicular to the runway direction. At this level, a sufficient height between the surface and the expected vortex wake is covered by a rapid elevation scan. A corresponding angular range of, for example, 0 ° to 30 ° and a scanning speed of, for example, 10 to 20 ° / s can be selected by entering in a keypad. Then the elevation angle scan runs automatically.

To test the theoretically known vortex wake behavior in practice, an LD anemometer was installed on trial at Frankfurt Airport between runways 25L and 25R. The distance from the landing start was lanes about 260m. Furthermore, the same LD anemometer was set up for two weeks at the so-called "walking tip", which is 5 km outside the airport below the end of the runway 25L.

The scanning sequence is shown in FIGS. 10a and 10b. A program scan sequence begins with a fast elevation scan, for example between 2 to 20 ° and 18 ° / s and with a distance setting of 260 m. When passing an aircraft, a wake signal appears on the monitor. A vortex trail closer to the LD anemometer is tracked by a manually controlled reduction in distance. If the vortex position is closer than 100m, the azimuth direction is changed by 180 ° and the elevation scan continues on the opposite side of the LD anemometer. If the wake again reaches the scanning volume, it is now tracked by increasing the distance until it disperses. Such a measuring program can take several minutes.

The frequency spectra at the LD anemometer output contain the information regarding the velocity distribution in the measurement volume. Usually there is a peak that corresponds to the radial component of the wind vector (see Fig. 4). As soon as a vortex trail enters the sample volume, the wind peak becomes smaller or disappears and a complex signal structure appears. The maximum tangential velocity in the vortex can be derived from the position of the high-frequency flank. In Fig.lOc the simplified signature or time sequence is shown.

Fig.ll shows a computer printout of two scan seconds. Here, in Fig.ll in the ordinate direction, the time on the left and the elevation angle on the right and the line of sight speed v _LOS on the abscissa. The time was started on an airplane flyby, and the elevation angle scan was between 30 ° to 90 ° set. The scan time was 2s. A wake was measured close to 90 ° (from the "Gehspitz" site) and the wake speed was close to 8m / s. Due to the homodyne laser Doppler method, there is no sign of direction. Only the speed value is measured. The sign of the vortex speed can be obtained from knowledge of the normal wind speed and its direction.

In Fig.ll two different maximum wind speeds v _LOS , namely one close to the elevation angle of 70 ° and one close to the elevation angle of 80 °, are entered with a minimum in between. The minimum is the point where the sign changes (ie goes through zero). The two maximum speeds differ significantly from the normal wind prevailing there. The normal wind is added to the vortex component in the wind direction and subtracted from the other component against the wind direction.

FIG. 12 shows another computer printout for the same example shown in FIG. Here the wind and vortex trail peak values are printed out as a plus sign (+). The best fit for a theoretical model is printed in the form of circles (o). The mean speed is already subtracted, so that the two vortex peaks have the same speed. With the help of such a pattern recognition process, it is possible to determine a vortex development. The location of the vortex center can be determined and determined for each scan. With the help of additional data, such as the angular value and the distance, the computer can plot the height of the vortex center relative to the distance from the center line and the maximum tangential speed over the distance. As a result, the influence of aircraft landing on a runway with respect to traffic on one or or several parallel runways.

End of description

Claims (2)

1. Measuring device for determining the wind direction and wind speed in the atmosphere by means of a laser Doppler anemometer with a scanning mechanism, characterized in that only measuring values from a sector of approximately 100 ° and less of an azimuth scan are used to determine the wind direction and wind speed Multiple peak finders are supplied in which, in order to achieve a high processing speed, there is a fluid differentiation using digitally operating devices. 2. Measuring device according to claim 1, characterized in that for switching off the clouds, haze, fog and the like. influences of the multiple peak finders always pursue several frequency maxima, a preceding maximum being related to a subsequent maximum until the subsequent maximum is smaller than the previous maximum.

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